/* Yet Another Forum.NET
 * Copyright (C) 2003-2005 Bjørnar Henden
 * Copyright (C) 2006-2013 Jaben Cargman
 * Copyright (C) 2014-2020 Ingo Herbote
 * https://www.yetanotherforum.net/
 * 
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at

 * https://www.apache.org/licenses/LICENSE-2.0

 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
namespace YAF.Configuration.Pattern
{
    #region Using

    using System;
    using System.Web;

    #endregion

    /// <summary>
    /// Singleton factory implementation
    /// </summary>
    /// <typeparam name="T">
    /// </typeparam>
    public static class PageSingleton<T>
        where T : class, new()
    {
        // static constructor, 
        // runtime ensures thread safety

        #region Constants and Fields

        /// <summary>
        ///   The _instance.
        /// </summary>
        private static T _instance;

        #endregion

        #region Properties

        /// <summary>
        ///   Gets Instance.
        /// </summary>
        public static T Instance => GetInstance();

        #endregion

        #region Methods

        /// <summary>
        /// The get instance.
        /// </summary>
        /// <returns>
        /// </returns>
        private static T GetInstance()
        {
            if (HttpContext.Current == null)
            {
                return _instance ?? (_instance = (T)Activator.CreateInstance(typeof(T)));
            }

            var typeStr = typeof(T).ToString();

            return (T)(HttpContext.Current.Items[typeStr]
                       ?? (HttpContext.Current.Items[typeStr] = Activator.CreateInstance(typeof(T))));
        }

        #endregion
    }
}